WARBLER SONGS. 



IN the development of birds away from the primitive 

 reptilian tj'pe, there has been, in general, a tendenc}^ to 

 decrease in size as well as to structural modifications brought 

 about by changing environment. In order to increase greath^ 

 in numbers there must be a decrease in size if the world were to 

 contain the host. Along with decrease in size there .seems to 

 have developed a tendency to vocal expression, culminating at 

 the present day in utterances second only to speech — song. 

 We are unable to attribute to a bird's vocal utterances, how- 

 ever complex they may seem, more than a momentary state of 

 feeling, unless it be taught by man. Only the vSmaller birds 

 truly sing ; the muscles of their syrinx enabling them to give 

 utterance to ^'aried notes instead of a monotonous repetition of 

 the same note. 



In the higher development of the Oscines — the singing 

 birds — there naturally grew differences in song just as there 

 grew differences in .structure and habits, producing more or 

 less well defined groups. We might reasonably expect that 

 if a group be sharply marked off from other groups structur- 

 ally its style of song would al.so be sharply marked ; that it 

 would possess a distinct song-type ; and if there be gradations 

 between groups there would naturally be gradations in song 

 likewise. In general we find this to be true, but in particular 

 there are exceptions. Thus, while the Warblers certainly 

 possess a song-type it distinctly grades off to the Sparrows, 

 which are not otherwise closel}- related to them. So we are 

 forced to find and define the song-type and work both ways 

 from it out to the limits, and there .seek to di.stingui.sh cer- 

 tainly between the two which .seem to grade into each other. 

 The warbler song-tj'pe may be defined as a high pitched, 

 hissing whistle consisting of two well defined parts, usually- 

 on a different pitch. There are many and decided departures 

 from this type, the one extreme being a monotonous repetition 



